Data for trends in prevalence of asthma, allergic rhinoconjunctivitis, and eczema
over time are scarce. We repeated the International Study of Asthma and Allergies
in Childhood (ISAAC) at least 5 years after Phase One, to examine changes in the prevalence
of symptoms of these disorders.
For the ISAAC Phase Three study, between 2002 and 2003, we did a cross-sectional questionnaire
survey of 193,404 children aged 6-7 years from 66 centres in 37 countries, and 304,679
children aged 13-14 years from 106 centres in 56 countries, chosen from a random sample
of schools in a defined geographical area.
Phase Three was completed a mean of 7 years after Phase One. Most centres showed a
change in prevalence of 1 or more SE for at least one disorder, with increases being
twice as common as decreases, and increases being more common in the 6-7 year age-group
than in the 13-14 year age-group, and at most levels of mean prevalence. An exception
was asthma symptoms in the older age-group, in which decreases were more common at
high prevalence. For both age-groups, more centres showed increases in all three disorders
more often than showing decreases, but most centres had mixed changes.
The rise in prevalence of symptoms in many centres is concerning, but the absence
of increases in prevalence of asthma symptoms for centres with existing high prevalence
in the older age-group is reassuring. The divergent trends in prevalence of symptoms
of allergic diseases form the basis for further research into the causes of such disorders.